Bicycles generally work when bicyclists manually and rotatably push on pedals attached to cranks which are connected to the rear bottom bracket axle or spindle with front and rear driving brackets coupled by a chain between the two bottom brackets. In order for bicycles to function properly, appropriate tension of the chain has to be maintained. Even though it may be impractical to fine tune the chain length or tension precisely, slight repositioning or adjustment of the chain tension utilizing certain components is highly desired. By repositioning or adjusting a component of a bicycle, chain tension can be optimized for installing and maintaining the chain. It is a well-known and conventional practice to periodically adjust the rotational axis of the front pedal crank spindle or the rear pedal crank spindle, on which the front and rear driving sprockets are mounted. One of the adjusting components for adjusting the chain length or chain tension of a bicycle is an eccentric mount, which is an assembly in which the rotational axis of the spindle is eccentric to a cylindrical casing or a shell that is rotatable for positional adjustment within the shell of the bottom bracket portion of a bicycle frame.
Typically, the term “eccentric” refers to a wheel that rotates on an axle or spindle bringing about a mechanical motion to operate as a crank or a cam by an attachment to the wheel. This term “eccentric” is commonly used as a cylindrical part for bicycles, particularly for placing the part through the bottom bracket inner shell of a bicycle. The term “bottom bracket” refers to the part of the bicycle frame around which the pedal cranks rotate and also includes other bearings and axle/spindle components such as pedal shafts which run through this bottom bracket inner shell of the bicycle frame. Eccentrics are typically used to adjust the tension of the chain on a bicycle, when the eccentric is rotatably adjusted, the chain is tightened or loosened. An eccentric, positioned in the bottom bracket inner shell, also has an opening or a bore in which the pedal crank assembly or pedal shaft is snugly placed for bicyclists to generate motion by rotatably pushing on the pedals attached to cranks with pedal shafts running through the bore which are securely fastened to the eccentric in the bottom bracket inner shell.
There are different mechanisms for adjusting the eccentric depending on the design of the shell of the bicycle and the eccentric being used. The first design of adjusting the eccentric is by placing the eccentric into the loose bottom bracket shell of the bicycle frame. In this mechanism, the shell is a split shell. After placing the eccentric into the loose bottom bracket shell, the outer shell can be tightened to close any gap of a split shell by utilizing pinch bolts to tightly engage the eccentric to the inner shell. An easy way to conceptualize this mechanism and assembly is to look at bicycles on which the conventional pinch bolts are used to adjust the height of a seat post by loosening or securing the seat tube with small, movable handles on the frame near the seat tube. The second mechanism of adjusting the eccentric is to use a setscrew whereby a screw can fit around and through the outer portion of the shell to tightly engage the eccentric to the inner shell of the bottom bracket. The first design of using pinch bolts requires designing the bicycle with a split shell which results in higher labor and manufacturing costs. The second design requires bicyclists to prepare for situations whereby chains can become loose or undone in a remote location. To prepare for such events, bicyclists are subject to unnecessarily carrying heavy tools which is not feasible nor preferable, particularly for weight-sensitive bicyclists.
A bottom bracket assembly mechanism using a wedge bolt is taught in the U.S. Pat. No. 4,808,147 (the “'147 patent”) and U.S. Patent Application Publication No. US2006/0189426 A1 (the “'426 publication”), to Graham and Dodman et al., respectively. Both of these references are directed to an adjustable eccentric bracket assembly for a bicycle using a wedge bolt. Both of these references disclose assemblies limited to particular purposes.
The '147 patent, for example, is directed to an eccentrically mounted pedal crank spindle that is rotatably adjustable in the inner surface of the shell of the bottom bracket of a bicycle frame. The assembly taught in the '147 patent comprises a body member with a major portion having a circular cylindrical external surface that can fit with the inner surface of the shell. The remainder of the external surface of the body member is a flat wedge surface obliquely oriented to the axis of the cylindrical surface to coextensively adapt to a wedge member. The solid wedge member has a circular external cylindrical surface with the same diameter of the body member and a wedge surface that is complementary to the body member. The '147 patent teaches a drive mechanism of rotatably screwing a wedge driver in which the wedge member is displaced laterally to tighten within the inner surface of the shell of a bicycle frame. Even though this assembly solved the problems mentioned in the prior art, the solid, planar, and cylindrical surface of the body member and the solid wedge surface of the wedge member contribute to overall weight of the assembly. Furthermore, the assembly oftentimes contributes to sticking of the wedge to the single planar, flat wedge surface when the wedge is being loosened to adjust the position of the assembly in order to adjust the chain of a bicycle.
The '426 publication is directed to a similar bracket assembly with two wedge members with two external surfaces of the body member which is obliquely oriented to the axis of the cylindrical surface rather than using a single wedge member complimentary to the body member. The eccentric body member also has an external outer cylindrical surface that is provided in close fit with the inner surface of the shell of the bicycle frame. The wedge members are provided to co-act with the body member to alternatively tighten or loosen the body member with respect to the inner shell of the bicycle frame. The body member and the wedge members are similarly provided as in the '147 patent with complimentary wedge surfaces. The wedge members are laterally and perpendicularly displaced relative to the body member to tighten or loosen the fit within the inner surface of the shell. Despite the fact that the overall weight of the bracket assembly is somewhat reduced, the assembly taught in this publication is not designed to accommodate the frictional resistance necessary to sustain and prevent slipping from the correctly adjusted position of the bottom bracket assembly to the inner surface of the shell of the bicycle frame.
Therefore, a design of an eccentric bottom bracket assembly is necessary that further reduces the overall weight of the assembly and provides overall strength and longevity to endure years of wear and tear. A design of an eccentric assembly is also necessary to allow a bicyclist to easily adjust the position of the eccentric bottom bracket assembly when the chain comes undone in a remote location leaving a bicyclist with limited access to tools. An eccentric bottom bracket assembly is also desired that can be universally mounted on any bicycle and utilized from either sides of the bicycle. An eccentric bottom bracket assembly is also desired that is easily adjustable without the jamming of any portion of the assembly within the inner surface of the shell of a bicycle frame.
The present invention is directed to overcoming the foregoing and other disadvantages. More specifically, the present invention is directed to a new and improved eccentric bottom bracket assembly for a bicycle frame on an eccentrically mounted spindle that is rotatably adjustable.